Adventures in Paleontology

By Thor Hansen and Irwin Slesnick Illustrations by D.W. Miller

Arlington, Virginia

Claire Reinburg, Director Judy Cusick, Senior Editor Andrew Cocke, Associate Editor Betty Smith, Associate Editor Robin Allan, Book Acquisitions Coordinator PRINTING AND PRODUCTION Catherine Lorrain, Director Nguyet Tran, Assistant Production Manager Jack Parker, Electronic Prepress Technician Will Thomas, Jr., Art Director NATIONAL SCIENCE TEACHERS ASSOCIATION Gerald F. Wheeler, Executive Director David Beacom, Publisher Copyright © 2006 by the National Science Teachers Association, 1840 Wilson Blvd., Arlington, VA 22201. www.nsta.org All rights reserved. Printed in the United States of America. 09 08 07 06 4 3 2 1 LIBRARY OF CONGRESS CATALOGING-IN-PUBLICATION DATA Hansen, Thor A. Adventures in paleontology : 36 classroom fossil activities / by Thor Hansen and Irwin Slesnick ; illustrations by D.W. Miller. p. cm. Includes bibliographical references. ISBN-13: 978-0-87355-272-1 1. Paleontology--Study and teaching (Middle school)--Activity programs. I. Slesnick, Irwin L. II. Title. QE715.H36 2006 560.71’2--dc22 2006003510 NSTA is committed to publishing material that promotes the best in inquiry-based science education. However, conditions of actual use may vary, and the safety procedures and practices described in this book are intended to serve only as a guide. Additional precautionary measures may be required. NSTA and the authors do not warrant or represent that the procedures and practices in this book meet any safety code or standard of federal, state, or local regulations. NSTA and the authors disclaim any liability for personal injury or damage to property arising out of or relating to the use of this book, including any of the recommendations, instructions, or materials contained therein. Permission is granted in advance for photocopying brief excerpts for one-time use in a classroom or workshop. Permissions requests for electronic reproduction, coursepacks, textbooks, and other commercial uses should be directed to Copyright Clearance Center, 222 Rosewood Dr., Danvers, MA 01923; fax 978-646-8600; www.copyright.com.

Featuring sciLINKS ®—connecting text and the internet. Up-to-the-minute online content, classroom ideas, and other materials are just a click away.

Figures 2.12, 2.16, 2.17, 2.28, 2.41, and 7.3 adapted from Dinosaurs, by D. Norman, J. Sibbick, D. Blagden, and D. Nicholls. Random House, 1996. Figure 6.9 adapted from a photo in Dinosaurs, An Illustrated History, by E. H. Colbert, Hammond World, 1983.

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Introduction ..................

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Chapter 1: How Do Fossils Form? 1 Activity 1, Making a mold and cast ................................................................................................................ 2 Activity 2, Making a mold and cast of your teeth ........................................................................................... 3 Act ivity 3, Simulating permineralization ....................................................................................................... 4 Activity 4, Molecule-for-molecule replacement of fossils .............................................................................. 5 Activity 5, Fossils in strata............................................................................................................................... 6 Activity 6, Inventing ways to make fossils of grapes and bananas .................................................................. 8 Activity 7, Fossils in amber ............................................................................................................................. 9 Introduction .....................

Chapter 2: What Can You Learn From Fossils? Introduction: Scientific Inquiry ....................................................................................................................13 Activity 1, Inferring the characteristics of people from their hands .............................................................17 Activity 2, Reconstructing Scaphognathus crassirostris ...................................................................................20 Activity 3, Restoring Scaphognathus crassirostris ............................................................................................23 Activity 4, Tracking dinosaurs.......................................................................................................................24 Activity 5, Weighing dinosaurs ....................................................................................................................31 Activity 6, Learning the bones ......................................................................................................................33 Activity 7, Hatching and death on Egg Island ..............................................................................................36

40 Activity 9, What was the purpose of the plates on the back of Stegosaurus? ................................................42 Activity 8, Predation .....

Chapter 3: Mass Extinction and Meteor Collisions With Earth 49 Activity 1, Searching for micrometeorites ....................................................................................................53 Activity 2, Calculating the energy of incoming rocks from space ................................................................54 Activity 3, Modeling impact craters..............................................................................................................55 Introduction ...................

Activity 4, What happens to Earth when the energy of an asteroid or comet is released in the rock and atmosphere of Earth? ...............................................................................57

Chapter 4: How Are Fossils Collected and Prepared? 59 Activity 1, Preparing a fossil fish ...................................................................................................................60 Introduction ...................

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Activity 2, Making fossil replicas ..................................................................................................................63

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Activity 3, Microfossils ..

Chapter 5: How Can You Tell the Age of Earth? 69 Activity 1, The duration of time since Earth was formed .............................................................................70 Introduction ...................

Chapter 6: How Did Dinosaurs Evolve? 73 Activity 1, Archaeopteryx, Compsognathus, and Gallus domesticus ................................................................74 Activity 2, Homology .... 77 Activity 3, The method of cladistics .............................................................................................................81 Activity 4, Rates of evolution of Ceratopsia and contemporary reptiles ......................................................86 Introduction ...................

Chapter 7: Diversity, Classification, and Taxonomy Introduction ...................

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Activity 1, The ages of the reptiles, the archosaurs (dinosaurs, pterosaurs, and crocodiles), and the theraspida (mammals) .........................................................................90 Activity 2, How big was Ultrasaurus macIntosh? ............................................................................................94 Activity 3, The worldwide distribution of dinosaurs.....................................................................................96 Activity 4, Measuring diversity .....................................................................................................................99

Chapter 8: Fossils in Society 105 Activity 1, Coal, petroleum, and natural gas ............................................................................................. 106 Activity 2, Making thin peels of coal balls to view ancient plants ............................................................ 108 Introduction ................

Chapter 9: When Are Fossils Art? 111 Activity1, Dinosaur art contest .................................................................................................................. 112 Activity 2, Fossil works of art ..................................................................................................................... 114 Glossary ....................... 117 Index ........................... 123 Introduction ................

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t one point or another, it seems like all students are interested in paleontology. Wonderful extinct animals like dinosaurs excite the imagination like almost nothing else. Once you have the students’ interest, you will find that a study of paleontology provides avenues of exploration into a wide variety of foundational sciences such as biology, geology, chemistry, physics, and astronomy (See Table 1). Paleontology is also an excellent way to teach to the National Science Education Standards (NRC 1996), and all of the activities in this book are aligned with one or more of the Science Content Standards for grades 5–8 (See Table 2). We use an active hands-on approach because that is the best way to learn. A great teacher I know has a sign above his desk that reads, “If they hear it, they will forget. If they see it, they will remember. If they do it, they will learn.” It is the philosophy of this book that learning through hands-on activities is the best way to integrate new knowledge. The activities in this book are targeted primarily at teachers and students in grades 5–8 because studies have shown that these grades are a crossroads for students in regard to science. At this age many children decide whether or not they like science based on school activities, and unfortunately most decide that they do not. For example, the Third International Mathematics and Science Study (1999) showed that whereas only one country outperforms U.S. students in math and science at fourth-grade level, nine countries do so by eighth grade. We believe that engaging, inquiry-based, hands-on activities represent a vital way to capture the minds of these students. Though middle school grades are the primary audience for these activities, many of them have been used with both younger and older audiences. For example, I (Thor Hansen) regularly incorporate many of the activities in this book in my college classrooms with only minor modifications. This book comprises 36 different activities organized into 9 chapters. Chapter 1 (How Do Fossils Form?) discusses the ways that organisms become fossils and illustrates these concepts with activities that simulate fossil-making processes. Chapter 2 (What Can You Learn From Fossils?) explores what fossils can teach us about ancient organisms and also includes an explanation and activities using scientific inquiry. Chapter 3 (Mass Extinctions and Meteor Collisions With Earth) discusses the recent links that have been made between meteor and asteroid impacts on Earth and the demise of animals like the dinosaurs. Activities in this chapter include how to find real meteorites in your own yard and modeling the effects of meteorite impacts. Chapter 4 (How Are Fossils Collected?) describes some ways that fossils are found and prepared and guides the reader through the steps of preparing real fossil specimens. In Chapter 5 (How Can You Tell the Age of Earth?), students will make their own model for demonstrating the great age of Earth and the relative durations of important time intervals. Chapter 6 (How Did Dinosaurs Evolve?) explores the methods of cladistics and facilitates an understanding of evolution through active learning. Chapter 7 (Diversity, Classification, and Taxonomy) places fossils in the contexts of their distribution on the globe and how we name them and quantify their communities. Chapters 8 (Fossils in Society) and 9 (Fossils in Art) look at fossils from a humanistic perspective.

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Major scientific disciplines covered in each activity in this book. Number under “Activity” corresponds to chapter and activity number, e.g. “1-1” refers to Chapter 1, Activity 1. Abbreviations: Biol = Biology, Chem = Chemistry, Math = Mathematics, Phys = Physics, Geol = Geology, Astro = Astronomy, Ecol = Ecology, Evol = Evolution, Sci Meth = Scientific Method, Lng/Art = Language and Art. Activity 1-1 1-2 1-3 1-4 1-5 1-6 1-7 2-1 2-2 2-3 2-4 2-5 2-6 2-7 2-8 2-9 3-1 3-2 3-3 3-4 4-1 4-2 4-3 5-1 6-1 6-2 6-3 6-4 7-1 7-2 7-3 7-4 8-1 8-2 9-1 9-2

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Alignment of activities in this book to the National Science Education Standards (National Research Council, 1996). Columns refer to Content Standards A–G for grades 5–8. Number under “Activity” corresponds to chapter and activity number, e.g. “1-1” refers to Chapter 1, Activity 1. Abbreviations: Pers = Personal, Perspect = Perspectives.

Activity 1-1 1-2 1-3 1-4 1-5 1-6 1-7 2-1 2-2 2-3 2-4 2-5 2-6 2-7 2-8 2-9 3-1 3-2 3-3 3-4 4-1 4-2 4-3 5-1 6-1 6-2 6-3 6-4 7-1 7-2 7-3 7-4 8-1 8-2 9-1 9-2

A Science as Inquiry

B Physical Science

C Life Science

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E F G Science & Science in Pers History & Technology and Social Nature of Perspect Science

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How Do Fossils Form? A fossil is any evidence of an ancient organism. The remains of the body, such as bones, shells, leaf impressions, etc. are called body fossils. The evidence of animal activity, such as tracks, trails, and burrows, are called trace fossils. Body fossils can be preserved: In an unaltered state where the hard parts such as shell or bone are relatively unchanged. In exceptional cases the organism may be mummified, frozen, or preserved in amber. ◆ By carbonization. This is indicated by a black film on an impression of the organism such as a leaf. This black film is the organic residue of the organism after its other material is removed or replaced by the fossilization process. ◆ By permineralization. In this case, pores of the skeleton of the organism (such as bone or wood) are replaced with mineral. Most petrified wood is preserved in this manner. ◆ By replacement. Original shell or bone undergoes an atom-by-atom substitution with another mineral. Pyrite (fool’s gold) is a common replacement mineral. The replaced fossil is usually a faithful replica of the original. ◆ By molds and casts. Here the original material dissolves leaving only impressions or infillings. Impressions of the interior or exterior of a fossil are molds. An infilling of the mold, so that an exact likeness of the organism is reproduced, is a cast. ◆

Topic: Fossils Go to: www.scilinks.org Code: AP001

TEACHER’S NOTES: Making a mold and cast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C H A P T E R 1 , A C T I V I T Y 1 This is a real crowd pleaser. It takes about 45–60 minutes and is a little messy, but produces beautiful impressions that students will want to keep. Hand out cups and leaves (or other material to be used as “fossils” such as feathers or shells) and have the students put their name on the bottom of the cup. Mix a large batch of plaster of paris with water to a fairly thick consistency for the first filling of each cup. You or the students should half-fill each cup. While they are arranging their “fossils” on the surface, make another batch of plaster with which to cover the fossil and fill the cup. This pause will allow the initial filling to firm up a little. Fill the cups to the top and let them harden before you try to crack them open (they will feel very warm). When the plaster is hard, peel off the paper and break open the plaster at the line of the fossils. Some of the blocks will be breakable by hand. Others will need a sharp rap on a table edge or they can be opened with a chisel or nail and a hammer.

Making a mold and cast of your teeth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C H A P T E R 1 , A C T I V I T Y 2 This is a variation of activity 1 which students find fascinating. How often do you get to see the inside of your own mouth? With a razor blade or Exacto knife, carefully cut around each paper cup about 1/2 inch up from base. Make the incisions parallel to the lip and leave about 1/2 to 1 inch uncut, producing a “hinge.” Hand out one to each student. While the students put the clay in the bottom of the cups and press their teeth into the clay, mix a batch of plaster of paris. The plaster should be a little thin so that it fills the cavities of their impressions. Make sure to let the plaster get good and hard before attempting to remove the clay because the points of the teeth will be fragile.

Simulating permineralization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C H A P T E R 1 , A C T I V I T Y 3 This activity produces a remarkably hard, rock-like “bone” out of an ordinary kitchen sponge. The sand it is buried in is also lightly cemented so that digging in it is like digging up a real fossil.

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Making a mold and cast M AT E R I A L S : ◆ paper cup ◆ stirring stick ◆ plaster of paris ◆ hammer and nail ◆ large plastic bowl or tub for mixing plaster ◆ leaves, feathers, or other “fossils”

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Procedure: Put your name on the bottom of the paper cup. Half fill the cup with plaster of paris. Press the leaf, feather, or other object you want “fossilized” onto surface of plaster. Do not submerge the leaves in the plaster, but make a layer sitting on the surface. The more of the surface that you cover with material the better. Wall-to-wall leaves (or feathers, or whatever) make it easier to split the plaster block later. Also if some of them touch the sides of the cup it makes it easier to see where the splitting point should be. Add plaster to near the top of the cup. Be careful as you pour the second layer of plaster. If the first layer is still very fluid, pouring the second layer may cause the two layers to mix and to jumble the leaves. You want the leaves to be on a flat surface, parallel to the table (perpendicular to the walls of the cup). For this reason, it is best to pour the first layer, lay on the leaves, and then wait a few minutes for the first layer to set a little before pouring the second layer. If you make the plaster fairly thick, it will set more quickly. After the plaster hardens (10–20 minutes, it will undergo a chemical reaction that produces heat), tear off the paper cup and use the hammer and nail (like a chisel) to split the plaster block at the layer made by the leaves to reveal the mold.

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Making a mold and cast of your teeth M AT E R I A L S :

Procedure: Press clay into lower portion of the cup. Press upper teeth into clay as deeply as possible (you are making a mold), being careful not to damage edge of cup. Rejoin edges of cup and tape over the incision. Use as much tape as necessary to completely seal the cut. After the halves of the cup are rejoined and taped, put the cup onto newspaper or on a tray before the next step, because if the tape seal is not tight, plaster will leak out of the cup. Pour plaster of paris into the cup (make it to a fairly fluid consistency, so air bubbles can be released more easily) and rap the base of cup several times on tabletop (this is to dislodge bubbles that may be trapped in the crevices). When the plaster has set (it should be good and hard), tear away cup and carefully peel clay away from the plaster to reveal a cast of your teeth.

◆ paper cup ◆ tape (masking or duct tape, scotch tape is not as good) ◆ non-toxic modeling clay or plasticene ◆ sharp knife (Exacto knife or scalpel is good. Be careful!) ◆ plaster of paris ◆ plastic container for mixing plaster.

FIGURE 1.1 Steps in making a cast of your teeth. Left: Cut paper cup, leaving a small section intact for a hinge. Middle: Fill with clay to the top of the cut and impress teeth. Right: Tape cup together tightly and add plaster.

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Simulating permineralization M AT E R I A L S : ◆ two bowls ◆ sand ◆ ordinary kitchen sponge ◆ salt ◆ warm water ◆ scissors ◆ spoon

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After an organism is buried and its flesh has rotted away, only the skeleton or shell is left. Some of these hard parts, such as wood or bone, are porous, meaning they are filled with tiny holes. When water in the ground flows through these pores, the water leaves minerals that fill up the pores and turn the fossil into rock. This process is called permineralization and is the way petrified wood and much bone is preserved. One of the most common minerals to fill wood and bone in this way is silica. Cut and polished silicaized (agatized) wood and bone is very colorful and beautiful.

Procedure: Cut a piece of the sponge into a bone shape and bury it in sand in the bowl. Mix 2 parts salt to 5 parts warm water (e.g. 100 ml of salt to 250 ml of water) and pour the salt water into bowl (enough to completely soak the sand). Set bowl in a warm/sunny spot, under a hot lamp or in a low temperature oven (at around 250 degrees Fahrenheit, be sure to use a Pyrex bowl if you apply heat) and allow water to evaporate. In the oven, the block will dry in a few hours. If left out in the sun, it may take several days. Once dry, use the spoon to excavate your fossil. The sponge is hard because it soaked up the salty water and as the water dried, it left salt crystals in the pore spaces of the sponge. This is like permineralization: the manner in which most wood and bone is fossilized.

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Molecule-for-molecule replacement of fossils Sometimes the chemical composition of a fossil changes due to conditions in the environment. For example, a bone that is buried in salty mud may have its open spaces fill with a particular salt. The bone will have been “permineralized.” Original bone may remain around the spaces. At a later time the molecules that make up the original bone may be replaced by molecules of an entirely different and more stable substance. Fossilized wood or bone often forms in this way. The appearance— and even the microscopic structures of such tissues as bone and wood—is caused by molecule-for-molecule replacement. Many of the attractive shells of fossil mollusks are composed of replacement minerals much different from the original carbonate. A dramatic example of this phenomenon is the carbonate shells or ammonites that have been replaced by iron sulfide, or pyrite (fool’s gold), giving the fossil the appearance of having been made of gold. Fossilization by replacement can be demonstrated by a simple activity.

M AT E R I A L S : lustrous steel wool (no coating) ◆ steel wire ◆ copper sulfate crystals ◆

Procedure: Form the wire into the shape of a person about three inches high. Fill out the body with puffs of steel wool. Make a 2% solution of copper sulfate. Fill a container with copper sulfate solution so that you can immerse the little fellow up to its waist. In a few seconds the steel (iron) will F I G U R E 1 . 2 begin being replaced by the copper in the solution and Wire figure used to simulate replacement. the iron will take the place of copper in the solution. In the end the copper fossil person is structurally identical to the original steel person.

Iron

Copper

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Fossils in strata M AT E R I A L S : ◆ sand ◆ plaster of paris ◆ container ◆ “fossil” material, such as sand, dirt, gravel, shells, etc.

Topic: Sedimentary Rock Go to: www.scilinks.org Code: AP002

Fossils occur in sedimentary rock, which is rock that is composed of grains (such as sand or clay) that were laid down by water or wind. The mud or sand in a stream, lake, or desert may someday become deeply buried and turn into sedimentary rock. Sedimentary rock has layers or strata that reflect the natural rhythm of weather and deposition. For example, a stream flowing normally is usually clear because slowly moving water cannot move rocks or carry much sediment. But when the stream is flooding the water is higher and faster, and is brown because it is carrying more sand and clay. It is probably also carrying sticks and leaves and perhaps a dead animal. If the stream rises so much that it overflows its banks, it will deposit its load of sand, clay, sticks, and leaves in a layer on top of the stream banks. This layer of sand and debris is a sedimentary record of a flood event. Over time many such storms will leave a thick sequence of strata that records the history of the stream and its floods. Different sedimentary environments have different types of deposits. For example, a beach deposit will typically consist of sand and seashells. A stream deposit may have sand, gravel, sticks, and leaves. A forest floor will have soil and plant debris. When sediments are deposited, new layers are always laid on top of older ones. So in a stack of such layers, the youngest layer lies on top and the layers get progressively older as you go down. You can make simulated sedimentary rock with fossils and have your own “dig” where you unearth and reconstruct past environments.

Procedure: Go to several different sedimentary environments and observe the conditions you find there and collect some sediment. You might go to a beach and collect some sand and shells and perhaps a small piece of driftwood or a bird feather. You might also collect material at a pond, a meadow, a lake, or a forest. Collect some sediment or soil from each and try to find some distinctive items that will identify the environment such as leaves, fish bones, seashells, and so on. Figure out what geologic “story” you want to tell. For example one story might record what happens when sea level rises over a forest. This would involve a forest deposit overlain by a beach, overlain by deeper water sediments. As sea level falls, you might then expect to see another beach overlain by stream or forest deposits again. To make a sedimentary record of this sequence of events, first take a watertight container like a large plastic milk bottle or cardboard milk carton. Cut off the top and then put in layers of sediment that represent the different environments you want to portray. To portray the sea level rise and fall mentioned above, start by placing a layer of the “oldest” environment (forest soil) at the bottom of the carton. Place over this a layer of beach deposits and some broken shell (as you might find on

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a beach), followed by some finer sediment and more shells to represent the deeper water of the sea. The sea level fall would be the reverse of this, i.e., laying another beach layer over the deep water sediment and that in turn would be overlain by more forest or maybe a stream deposit. Try to place as many “fossils” and other interesting artifacts (feathers, fish or chicken bones, bottle caps, coins) in the mix as you can. You could even add a layer of modeling clay that had “tracks” in it. Once you have placed all the layers in the container, you can turn this sedimentary sequence into “rock” by making a dilute mixture of plaster of paris and water (about 3 tablespoons of plaster to 1/2 cup of water) and adding it to the sediment in the container. Slowly pour the liquid into the container until the whole thing is saturated. Let the block dry completely; at least one to two days, depending on the size of the container. Once dry you can cut or peel away the container and see the layers from the side exactly the way they would look if you were at a real rock outcrop. The dried mixture should be firm enough to be rock-like but soft enough to easily dig with a spoon or butter knife. In the classroom students should each have a brush and a digging tool. As they work from the top of the block down, they should describe the sediment, retrieve the “fossils” and identify and label them and place them in small containers just like a real paleontologist. An entry in their notes might look like this: Layer 1—Sand and gravel with leaves and a small bone. Probably a stream deposit. Layer 2—Fine sand with whole and broken seashells. Possibly a beach deposit, etc. Once they have excavated the entire block, they can reconstruct the sequence of events that took place. Remember the actual sequence is the REVERSE of the order in which they were excavated. In other words, the last or most recent event that happened is represented by the top or first layer that was excavated and the first or oldest event is at the bottom of the block.

FIGURE 1.3 Making simulated fossils in strata. Left: Fill cardboard or plastic carton with layers of sediment and “fossil” objects. Middle: Add dilute plaster mixture until thoroughly soaked. Right: After it dries, peel away sides of container and excavate.

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Inventing ways to make fossils of grapes and bananas M AT E R I A L S : ◆ fresh grapes ◆ banana ◆ shrimp ◆ fish ◆ cubic foot of forest floor litter and soil.

Plants, animals, and microorganisms have life cycles. They come into being, live for a while, and then die. There are no known exceptions. In this activity you will investigate what can happen to the remains of organisms when they die. In the second part of the activity, you will investigate alternative ways you can preserve a dead organism so that evidence of its existence will last indefinitely. Objectives of this activity are to 1) observe and record the physical and chemical changes in the body of a dead organism over a period of time, 2) explore and describe the dead organism in a cubic foot of litter and soil from a forest floor, and 3) devise ways to preserve evidence of the existence of your dead organism.

Procedure: Obtain about a dozen fresh grapes and/or a banana. Imagine that these fleshy fruits represent even larger fleshy dead organisms. ◆ Place one grape and/or one slice of banana in an open dish. Observe what happens to these “dead organisms” over a period of several months. ◆ Place a cubic foot of forest floor litter and soil on a large sheet of butcher paper. Beginning at the top of the cube, carefully remove each layer of material. The top layer should be the most recent accumulation of leaves, twigs, lichens from the over-hanging trees. As you go deeper into the cube you should encounter increasingly older plant material. Using pictures describe the fate of plant materials that fall onto the forest floor. ◆ Select other grapes or pieces of bananas. How many different ways can you preserve the fruit so that your descendants one million years from this day will have at hand evidence of the existence of your grape or banana slice? In a sense you will manufacture a fossil. ◆

Analysis: What was the fate of exposed grapes and banana slices? ◆ What appears to be the fate of dead materials that accumulate on a forest floor? ◆ List the ways you, and others, were able to produce fruit fossils from fresh grapes and banana slices. ◆ Fossils you made from fresh fruit are artificial in the sense that the preservation was manmade and not the way fossils form in nature. Under what circumstances do you think fossil grapes and bananas might form in nature? ◆

Going Further: For various reasons, most human cultures do not allow dead bodies to lie around and decompose. A large human industry manages the disposal of dead people, pets, or other organisms. Which methods of disposal of bodies recycle them? Which methods tend to preserve bodies and thus create artificial fossils?

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Fossils in amber Interest in amber has soared since the book and movie, Jurassic Park, captured the imagination of the public. In the story scientists found Jurassic Period mosquitoes in amber that had sucked the blood of dinosaurs. By collecting the blood of the dinosaurs and amplifying the DNA in the white blood cells, the scientists were able to produce the animals from which the blood was taken. As a result, the scientists populated an entire island with extinct animals. Real life later copied fiction when scientists extracted DNA from insects in amber from ancient ages. Dr. Raúl Cano of California Polytechnic State University and colleagues reported having extracted and sequenced DNA from a weevil embedded in amber from the age of dinosaurs (1993). Dr. Cano also caused excitement when he reported having cultured live symbiotic bacteria from the abdomens of stingless bees preserved in 40 million year old amber from the Dominican Republic (1994). In this activity you will polish a piece of rough amber to a clarity that will enable you to see fossil inclusions. Only rarely will you find a flower or an insect in amber. However, it is rare to find a piece of amber that does not contain some trace of past life.

M AT E R I A L S : ◆

specimen of rough amber

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80-, 280-, and 600-grit sandpaper

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cerium oxide polish

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denim cloth for polishing

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Procedure: Begin using 80-grit sandpaper if the rough amber is jagged and coarse. Wear the amber ore down to expose the yellow-orange amber on all sides. Use 280-grit sandpaper to expose at least two surfaces of your amber. Round off the sharp edges of your piece. Use 600-grit sandpaper to polish the specimen to a shine. Dampen the swatch of denim cloth with water, and lightly sprinkle the amber with cerium oxide, or other jeweler’s polish. You can use toothpaste in place of cerium oxide. Polish the sanded piece of amber until the clear faces of the specimen are free of scratches. Examine the polished piece of amber with a dissecting microscope, or thin slices with a compound microscope. Use 10x or 20x hand lenses for spot checks. When you find an interesting inclusion, record sketches of it, from several angles, on drawing paper. The organisms of the Cenozoic Era (about 65 million years ago to the present) are not so different from the insect and plants of today that you can’t identify them to family and often to genus. If you have a piece of rough copal—a specimen much younger in age than amber—you should proceed to polish it in the same manner as the amber. The finished product can be used for science study, or for a pretty gift for a loved one.

What is amber? Amber is fossil resin secreted by tropical flowering and conifer trees in response to wounds inflicted by boring insects, mechanical injuries, or just growth. Resins apparently provide a mechanism for sealing bark wounds and inhibiting an attack by insects and herbivores.

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FIGURE 1.4 Insect being trapped in tree sap that will eventually become amber. Drawn by Hazen Audel.

Resin also inhibits the growth of bacteria and fungi. Unlike gums, resins are not water soluble. Under conditions of moderate temperature, pressure, absence of air, and probably submergence in seawater, resins can remain intact in sediment for hundreds of millions years. Chemically, amber is a mixture of terpenoids that make up the resin and which forms after approximately 4 to 5 million years of polymerization and oxidation. Before becoming amber, the resin is in a form called copal. Resins become copal as soon as the resins lose their pliability. Fresh resin and copal from tropical rain forest are used today as a source of varnish. In the nineteenth century tons of Baltic amber were melted down for varnish. Resins should not be confused with sap, which is the water solution transported through the xylem and phloem (as maple syrup), or with gums, which are polysaccharides produced in plants as a result of bacterial infections. Ten percent of plant families produce resins, and most are tropical flowering plants. All conifers produce resins, but only pines and araucarians produce large quantities. The amber of the Dominican Republic and Mexico were produced by trees of the legume family of the genus Hymenaea. One of the major suppliers of modern resins in the tropics is a related species of Hymenaea. Amber of the temperate Baltic coast originated about 50 million years ago from the resins from the conifera family Araucariaceae. Evidence suggests that pine, once thought to be the major source of fossil resin, does not fossilize into amber. Since the infrared absorption spectrum of the conifer of Araucariaceae genus Agathis is dramatically similar to the spectrum of Baltic amber, many paleontologists think that Agathis, and not Pinus, represents the ancestral source of Baltic amber. Today, Hymenaea is distributed in South and Central America and Africa,

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and Agathis is distributed in parts of Asia, Europe, North America, and the West Indies. The dawn redwood Metasequoia glyptostroboides is a descendant of the ancient trees that produced amber in the Pacific Northwest about 50 million years ago. The process of amberization apparently requires that the polymerization of monomers (isoprenes) in fresh amber proceeds in decay-resistant environments, protected from the elements, inundated for a time by sea water, and never exposed the temperatures over 80 degrees Celsius or high tectonic pressures.

Inclusions in Amber Fresh amber on the trunk of a tree works like fly paper. As the organism sinks in, and as the resin continues to flow, the things that stick onto the resin become embedded before the glob of resin falls off the tree, or the tree rots away leaving just the resin (Figure 1.4). Inclusions reveal the diversity of forest life. In the 25- to 40-million-years-old amber found in the Dominican Republic, the resin entombed insects, spiders, frogs, feathers, leopard fur, flowers, bacteria, molds, mosses, rotifers, snails, leaves, buds, and a zillion unidentified pieces of debris including bubbles, now filled with gas and/or liquid. While the organisms died in the soft resin, standing waves from the frantic movement of an appendage can sometimes be seen in the amber. After death, internal parasites such as worms, or external parasites such as mites, can be seen leaving the host. Mold, often with fruiting bodies and spores, can be seen on the organic debris. But the resins are powerful antibiotics and decomposition of organic material is minimal. Some animals like long-legged spiders may leave a leg or two in the resin. A bird or a mammal brushing against the resin may leave a feather or a tuft of hair behind. As mammals trapped in the La Brea tars of California, or the dinosaurs in the mud of Tendaguru in East Africa, so too were the entrapped organisms in resins eaten away by predators and scavengers. Most Dominican Republic amber is clear and golden in color, allowing biological inclusions to be seen. In contrast, Baltic amber is often cloudy due to the large numbers of air bubbles in the resin. Popular colors of cloudy amber range from a milky golden to a chalky white depending on the size and the number of bubbles. Since amber melts readily (200–360 degrees Celsius), it absorbs color and oils, and accepts new inclusions easily. Altered amber can be made to appear more attractive than natural amber. Cano, R. J. 1994. Ancient bacillus DNA: A window to ancient symbiotic relationships? ASM News. 60(3): 129–134. Cano, R. J., H. N. Poinar, N. S. Pieniazek, and G. O. Poinar Jr. 1993. Enzymatic amplification and nucleotide sequencing of DNA from 120–135 million year old weevil. Nature 363: 536–538.

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What Can You Learn From Fossils? Scientific Inquiry What is scientific inquiry and how does it work? Scientific inquiry refers to the processes that help us to understand how the natural world works. (Note: This is different from the scientific method. The term scientific method is misleading, as there is no one “set-in-stone” approach to scientific research. Instead, scientists use a variety of approaches in their research, and are able to alter steps and go in new directions as the research demands. For example, penicillin, x-rays, and vulcanized rubber were all “accidental” discoveries, brought about because scientists altered the course of the research in response to unexpected findings.) There is nothing mysterious about scientific inquiry and we all use it everyday. It starts with facts that are objectively observable or measurable. We obtain these facts by observations of a natural phenomenon such as, “My car won’t start.” This initial factual observation might be followed by more information, like, “When I turn the key, nothing happens.” Based on these facts you form a hypothesis to explain why your car won’t start such as: “My battery is dead.” This hypothesis allows you to make some predictions such as: “If the battery is dead, my dome light will not work or will be dim. Also, my headlights won’t work or will be dim.” You can then test the hypothesis by checking your predictions; look at your dome lights and your headlights. If these lights all work fine, then it suggests the battery is not the problem. You could further test the dead battery hypothesis by replacing the battery with one that you know is good. If the car still does not start, then clearly the dead battery hypothesis has failed (or been falsified) and a new hypothesis must be formulated, e.g., “The starter motor is bad.” It is important to note here that all scientific hypotheses are tentative and must be discarded if they fail critical tests. In this case, it would be foolish to keep replacing the battery with new ones in the belief that the dead battery hypothesis must be right. It is also important to note that the hypotheses above invoke natural causes and are all testable. It would not be scientific to suggest a supernatural hypothesis such as: “My car is cursed” because this would not be testable. You cannot see or measure a curse and you cannot remove it to see if your car then functions properly. This is not to say that your car is not cursed, it is just that the statement “My car is cursed” is not scientific because it invokes a supernatural phenomenon that cannot be tested. Scientists propose hypotheses to explain many natural phenomena, such as why mountains form or why the Moon orbits Earth. When these hypotheses survive repeated tests by many scientists, they may be elevated to the status of scientific theory (e.g., Theory of Relativity, Theory of Evolution). Therefore a scientific theory is not just a guess or an opinion, it is a well-established scientific explanation for natural phenomena that has been tested many times and not falsified. A scientific law represents an even higher level of certainty. A scientific law is a statement of fact generally accepted to be true and universal

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Topic: Scientific Inquiry Go to: www.scilinks.org Code: AP003

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because they have always been observed to be true (e.g., the Law of Gravity, the Law of Thermodynamics). You can practice scientific inquiry with your class with a variety of props. For example bring in a table lamp and place it on a desk. You should “disable” the lamp by putting in a bad bulb or loosening the bulb and leaving it unplugged. Turn the lamp switch and asked the students to make observations, e.g., “the lamp does not work.” Now have them propose hypotheses for why the lamp does not work. For example: Hypothesis 1: The lamp is not plugged in. Hypothesis 2: The bulb is bad. ◆ Hypothesis 3: The bulb is not screwed in. ◆ Hypothesis 4: The electricity is not working. ◆ ◆

Now test each hypothesis by plugging the lamp in, screwing in the bulb, testing the bulb in another lamp, etc., until the correct hypothesis is found. The main points to be made here are that: 1. Scientific inquiry is not mysterious or intimidating, we all use it everyday. 2. Scientific inquiry deals only with observable natural phenomena and does not invoke supernatural causes. 3. Scientific inquiry is a series of processes and its conclusions are tentative. We must be willing to alter our hypotheses to accommodate new evidence.

TEACHER’S NOTES: The purpose of this set of activities is to enable student to engage in the same kind of investigative study as do paleontologists. Activities 1–3 progress from reconstructing an entire living human using evidence gathered from an examination of only that person’s hand, to the reconstruction and restoration of an authentic 150 million-year-old pterosaur fossil.

Reconstructing Scaphognathus crassirostris and Restoring Scaphognathus crassirostris . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C H A P T E R 2 , A C T I V I T Y 2 A N D 3 Important in the conduct of these activities is for the student to recognize that the reconstruction and restoration of the mystery fossil is authentic. They are solving the problem Georg August Goldfuss confronted in the 1820s. Goldfuss used the original fossil on a slab of limestone (Figure 2.3) to draw the bones in the skeleton (Figure 2.5). Two Goldfuss errors should noted: (1) Goldfuss miscounted the number of fingers with claws. There should be three on each forearm. We corrected this error. (2) This was the first specimen of Scaphognathus crassirostris discovered. It had no tail; and Goldfuss drew it without a tail. Later a specimen from the same limestone formation was found with a fully intact long tail.

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An assembled skeleton of Goldfuss’s Scaphognathus crassirostris appears in Figure 2.6 as students might assemble the bones. Few students can fully assemble the bones without help. The real or drawn skeletons of bats and birds and other vertebrates will help students figure out the sequence of appendage bone and vertebrae. Getting the giant finger in position often requires an intuitive leap. Restoring the living fossil and placing it in a suitable environment challenges the serious student to be scientifically accurate and imaginative at the same time. Figure 2.7 includes a sample of professional restoration of Scaphognathus crassirostris.

FIGURE 2.6 Reconstructed skeleton of Scaphognathus crassirostris.

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FIGURE 2.7 Life restoration of Scaphognathus crassirostris.

Question: What was the purpose of the plates on the back of Stegosaurus? .................... C H A P T E R 2 , A C T I V I T Y 9 This is a guided discussion activity that practices using scientific inquiry on a question about Stegosaurus. You might start by asking the question and then letting the students come up with as many different hypotheses as they can about the purpose of the plates. Then help them clarify what they mean about each hypothesis. For example if a student says the plates were for “defense,” you should ask them to give an example of a living animal that does this which will then allow you to make predictions to test these hypotheses. This activity is an example of how this discussion might proceed.

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Inferring the characteristics of people from their hands What can you tell about people by examining only their hands? How close could you estimate the person’s age? What clues would you look for in the appearance and texture of the skin, the condition of the fingernails, the feel of finger bones and joints, the behavior of the hand of the hidden person? What other characteristics of the person can you infer from the hand? This activity is a model of how paleontologists construct stories about fossils they find and study. In the model the hand is the fossil and the person behind the screen is the unknown organism from the past. Ordinarily, paleontologists know about as much about fossils and the whole extinct organism as you know about hands and people. The more you study the hands of people, the better you become in predicting what people are like by examining their hands.

Objectives:

M AT E R I A L S : ◆ mystery person ◆ dark cloth to cover a doorway with small slit for hand ◆ chair ◆ desk ◆ ruler ◆ magnifying glass ◆ clock with second hand

1. Observe, measure, and record characteristics of one hand of a person sitting outside your view. 2. Infer the characteristics of the whole mystery person and draw a composite picture.

Procedures: 1. Make a list of characteristics you can infer by examining the hands of people (Figure 2.1). Next to each characteristic describe the clues you will look for in the hand to give good ideas about the whole person. Perhaps you will do this planning the day before the hand of the mystery person enters your classroom through a hole in the sheet that covers the doorway. 2. After the hand appears at the doorway, examine the hand with your group. On the table with the hand should be some instruments for examining features of the hand: a magnifying glass to see the color of hair, a ruler to compare the finger lengths of the mystery hand and your own, and a clock with a second hand to compare the pulse of the hand with your own. Record your data. After returning to your seat, study your data. Then write a description of the mystery person, including its physical appearance, its behaviors and anything else you can infer. 3. After the class has discussed everyone’s observations and inferences, a class composite of the mystery person can be assembled. Since the mystery person represents a whole living fossil, something paleontologists never get to see, perhaps the activity would be more true to science if the class would never see the mystery person. The class will have to decide whether the mystery person (fossil) should ever show itself.

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Topic: Population Characteristics Go to: www.scilinks.org Code: AP004

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FIGURE 2.1 Students attempting to discern characteristics of a mystery person by his hand.

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Going Further: What can you infer about a nation by studying just the coins or stamps the government issued? What can archeologists tell about an ancient civilization by examining buried trash piles? What can police scientists infer from hair, blood, or auto tracks found at a crime scene? Examine the picture of the skeleton below. What can you infer about the biology of this animal from what you observe here?

FIGURE 2.2 Skeleton of a bat.

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Reconstructing Scaphognathus crassirostris M AT E R I A L S : ◆ scissors ◆ ruler ◆ transparent tape ◆ photocopy of exactsize fossil bones

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The fossilized remains of the animal illustrated in Figure 2.3 were found in a limestone quarry in Germany in 1826. About one hundred and fifty million years ago, the quarry was a deep ocean lagoon (Figure 2.4). Organisms that died and sank to the bottom of the lagoon were buried by fine particles of lime mud. Fine details of organisms were preserved in the limestone. Water currents did not redistribute skeletons. Georg August Goldfuss was the scientist who found the specimen. He cut out a slab of limestone with the fossil and took it to his laboratory for study. Goldfuss reconstructed the bones of the fossil animal, and then put the bones together to form a complete skeleton in a lifelike posture. The purpose of this activity is for you to try to solve the very same mystery Goldfuss confronted. What did the assembled skeleton of this fossil animal look like? And then: What kind of life did this animal live in Germany about G U R E 2 . 3 150 million years ago?

Original specimen of Scaphognathus crassirostris found by Goldfuss.

FIGURE 2.4 Reconstruction of lagoon environment in which Scaphognathus crassirostris was deposited.

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Objectives: 1. Reconstruct the skeleton of a mystery fossil from the Jurassic Period. 2. Make inferences about what the fossil animal looked like when alive, what food it ate, and its mode of transportation.

Procedure: 1. Cut out the life-size pictures of the mystery fossil’s bones as originally drawn by Goldfuss (Figure 2.5). 2. Use your knowledge about vertebrate skeletons and if available, the pictures of skeletons of such familiar animals as mammals, birds, and lizards. Begin your assembly at the head with the skull and jaw. Lay out the bones of the neck, chest, hip, and tail. Add the smaller leg bones to the hip. The thigh bone fits into the hip bone. A single leg bone connects with the thigh (you have two leg bones in each of your own legs). The small 4-toe feet connect with the leg bones. The larger upper arm bones connect with the shoulder blades. The lower arm bones are composed of two fused bones, to which the hand connects at the wrist. The fifth finger of each hand of the fossil is almost as large as its entire body. When your skeleton is assembled to your satisfaction, fix it in position by taping the bones together. You may wish to mount the model skeleton on a piece of poster paper.

Analysis: 1. How tall was the animal? __________ How wide was the animal when spread out? __ ________ Most animals barely float in water. Knowing the approximate volume of the animal and the density of water, what do you estimate the weight of the animal to be? __________ 2. What do you think was the function of the huge finger on each hand? 3. What modern animals do you think this fossil was most like? In what ways does it appear to have differed from modern animals that may live like it did? 4. What do the teeth in the skull and jaw tell you about feeding habits? How do you explain the large open spaces in the skull, the hollow long bones? The small feet with tiny claws and the large hands with large claws?

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FIGURE 2.5 Life-size picture of the fossil as originally drawn by Goldfuss.

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Restoring Scaphognathus crassirostris Once paleontologists have reconstructed the skeleton of a fossil vertebrate (Figure 2.6), they begin thinking about the appearance of the living animal, its habitat, how it lived with other organisms, and how it was adapted to its physical environment. In this part of the activity you have the opportunity to restore the fossil and put it into the environment to which it was adapted. For an example of the product of this approach see Figure 2.7.

Procedure:

M AT E R I A L S : ◆ crayons ◆ water paints ◆ poster paper ◆ clay

1. Look at the fossil skeleton for several minutes. Think about who this animal was, living around 150 million years ago in a tropical land by the sea now known as Germany. Measure the length of the head and the length of the body. Imagine how it might have moved about: For what purposes did it use the claws on its fingers? Was its skin bare, or was there a protective and/or insulating covering? 2. Now in the imaginative part of your mind pretend you and this beautiful beast are buddies. Spend a Jurassic day together: Travel together, eat together, double date. Become part of its life. Call it by its scientific name, Scaphognathus crassirostris. 3. Draw and color a scientifically accurate portrait of Scaphognathus crassirostris in a typical pose. Include in the background of the portrait evidence of its modes of locomotion, feeding behavior, and its habitat. You may wish to create a sculpture of the animal and include elements of its environment. See Figure 2.6 for an example of a reconstruction. 4. On the reverse of the picture, or on separate paper, make a list of questions about Scaphognathus crassirostris—questions you truly wish to answer.

Going Further: According to the latest counts, 20 families, 40 genera, and 100 species of pterosaurs have been discovered and described from the Triassic, Jurassic, and Cretaceous Periods. Scaphognathus was one of the 40 genera that included two species, Scaphognathus crassirostris and Scaphognathus purdoni. Pterosaurs ranged in size from the sparrow-like Anurognathus to the small airplane-sized Quetzalcoatlus. Pterosaurs lived for about 120 million years and were the dominant airborne vertebrates of the Mesozoic Era. Pterosaurs lived and died out with the dinosaurs. What can you find out about the evolution of pterosaurs? How did they relate with birds? How could the birds have survived the mass extinction crisis of 65 million years ago, but not the pterosaurs? What factors do you think contributed to pterosaur extinction?

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Tracking dinosaurs Tracks and traces are unique as fossils because they provide direct evidence of behavior in extinct animals. For instance, tracks can tell us if dinosaurs walked with their legs spread wide apart like a crocodile or closer together like a horse. Tracks can tell us how fast animals ran, or whether they traveled in herds. F I G U R E 2 . 8 There is even a trackway that suggests a dinosaur stampede! Trackway of a carnosaur and a hadrosaur. Let’s see how much we can tell from the dinosaur trackways at left (Figure 2.8): First, we can see that there are two trackways made by two different kinds of dinosaurs. We can also tell that both dinosaurs walked on two legs (bipeds) because the tracks are evenly spaced apart. The tracks of four legged animals (quadrupeds) tend to occur in pairs. You can demonstrate this by walking on a sheet of butcher paper with wet socks.

FIGURE 2.9 Human tracks made on paper. Top: walking normally. Bottom: walking on all fours.

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FIGURE 2.10 Tracks made by a hadrosaur, allosaur, ankylosaur, and sauropod.

First walk normally and see how the footprints are evenly spaced and occur along a line. Then walk on all fours and notice how the prints are paired and also spread apart laterally. You could get really fancy and make a tail to drag along, producing a tail-drag mark. Note that sauropod dinosaur trackways almost never show a tail-drag mark. What does this tell us about how sauropods held their tails? Use the Dinosaur Track Field Guide at right (Figure 2.10) to identify the dinosaurs that made the trackways on the previous page.

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FIGURE 2.11 Outline of a Tyrannosaurus rex footprint.

It is also possible to guess the size of the dinosaur that made a track. Generally the length of a dinosaur footprint was 1/4 the length of the leg (1/5 in the case of some of the skinnier bipeds such as the coelurosaurs). Since most dinosaurs walked with their backbones parallel to the ground, this is also a rough measure of their “height.” The largest Tyrannosaurus rex (tyrannosaur) footprint ever found was 34 inches in length. Make an overhead transparency of the footprint (Figure 2.11) and project it at actual size (34 inches long) to get a feel for just how big this is. What was the leg length of the dinosaur that made this print? How long was the tyrannosaur that made the track in Figure 2.11? This can be determined by comparing the leg length with the length of the body in Figure 2.12 below. The leg length is what fraction of the overall length? How long was the tyrannosaur that made the track?

FIGURE 2.12 Skeleton of an adult Tyrannosaurus rex.

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FIGURE 2.13 Human footprints. Top: spacing seen in a slow walk. Bottom: spacing seen in a fast walk.

Now try another demonstration with the butcher paper. First walk normally and then speed up. Notice how the footprints get farther apart with increased speed (Figure 2.13). Now how would you interpret the trackway below? What dinosaur made the tracks and what did it do? Putting everything we have learned together, how would you interpret the trackway below (Figure 2.15)? What dinosaurs made the tracks, how big were they, what happened?

FIGURE 2.14 Hadrosaur tracks indicating a change of direction and an increase in speed.

FIGURE 2.15 Hadrosaur tracks indicating change of direction and speed. Carnosaur tracks on intercept course and speeding up.

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Duckbill dinosaurs (ornithopods) are one of the few dinosaur groups where it is not obvious how they walked, i.e., on two or four legs. Their forelegs were large enough to reach the ground comfortably, so they could have walked on all four legs (quadrupedal, Figure 2.16) or on two legs (bipedal, Figure 2.17). Figure 2.18 is the track of a kind of ornithopod called a hadrosaur. What does this track tell us about how hadrosaurs walked? How would you interpret the trackway in Figure 2.19? FIGURE 2.16 With these tools, you can make Hadrosaur walking quadrupedally. additional scenarios, or have the students make their own. You can use the templates provided in the following figures to make your own tracks and lay them out across the floor. With their Dinosaur Track Field Guides and rulers, the students can identify the dinosaurs, calculate their sizes, and reconstruct their behavior.

FIGURE 2.17 Hadrosaur walking bipedally.

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FIGURE 2.18 Trackway of a hadrosaur.

FIGURE 2.19 Trackways of three sauropods; two adults and one juvenile.

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FIGURE 2.20 Footprint of a hadrosaur.

FIGURE 2.21 Left front (left) and left rear (right) footprints of the sauropod dinosaur Diplodocus.

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Weighing dinosaurs Tyrannosaurus may have weighed 7 tons. Brachiosaurus perhaps weighed 55 tons. Where do these figures come from? How can scientists calculate the weight of an extinct animal? One way is to just take a scale model of a dinosaur, measure the weight of the water it displaces and scale up for the dinosaur weight. Here’s the reasoning. All animals are about the same density as water. We are mostly composed of water, and the weight of the heavier parts like bone is offset by the air spaces in our lungs. You can test this by getting in a pool. If you take a deep breath and lie face down in the water, you will float. Most people will tend to sink when they exhale. Therefore we (and most other F I G U R E 2 . 2 2 animals) have a density near that of water [a density of 1.0]. So it stands to reason if you take an accurate scale model of a dinosaur, Apparatus used to measure the measure the weight of the water it displaces and then scale this volume of a dinosaur model. number up, you will get a reasonable estimate of the weight of the dinosaur. The tricky part is that a scale, say 1/40 scale, is a linear scale. It only measures one dimension, while a dinosaur is a 3-dimensional object. Therefore when you scale up the weight of your model, say 5 fluid ounces, you must multiply this number by 40 x 40 x 40, or 40 cubed, to get the approximate weight of the dinosaur. Of course the accuracy of your estimate is very dependent on the accuracy of the scale model. For example, if the reconstruction of the dinosaur in the model is too skinny, then the final weight estimate can be very far off.

M AT E R I A L S : ◆ watertight container ◆ pan to catch overflow of water ◆ dinosaur model

Procedure: 1. Place the watertight container inside of pan and fill the container with water to the very brim. 2. Now carefully place the dinosaur model into container, allowing the water to spill out into the pan. You should use a good quality scale model such as those produced by the British Museum or the Carnegie Institute if you want an accurate estimate. But any model will work. 3. Now carefully remove the container without spilling any additional water and measure the amount of water in the pan. This is the displacement of your model. You can use a standard measuring cup or one graduated in milliliters. A fluid ounce of water weighs close to one ounce (remember, a pint is a pound the whole world around) and a milliliter of waters weighs one gram.

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Now follow these calculations:

Topic: Using Models Go to: www.scilinks.org Code: AP005

Standard

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Displacement of model:

5 fluid oz.

148 milliliters

Weight of model:

5 ounces (approx.)

148 grams

Scale of model:

1/40

1/40

Weight scale cubed:

5 x 403 = 320,000 oz

148 x 403 = 9,472,000 gm

Est. dinosaur weight:

320,000 oz or 20,000 lbs.

9,472,000 gm or 9,472 kg

How to determine the scale of your model Good scale models will usually tell you the scale; the Carnegie and British Museum models are 1/40 scale. But if you don’t know the scale, or if you want to measure your own models, the scale is simple to determine. Measure the length of your model (lm) and divide that into the length of the dinosaur (ld). Length of model (lm) = 8 inches Length of dinosaur (ld) = 100 feet or 1,200 inches ld/lm = 150 or 1/150 scale

Going Further: Commercial models such as those by the Carnegie Institute, are made for normal adult dinosaurs at a 1/40 scale. So measuring the displacement of the Brachiosaurus model and scaling up by 40 cubed will give you the weight of a normal adult Brachiosaurus. It can be fun to estimate the weight of the largest dinosaurs such as Ultrasauros, Supersaurus, or Seismosaurus (or for other animals, such as whales) by changing the scale and using the appropriate model. An Ultrasauros is simply a huge dinosaur very much like a Brachiosaurus (Seismosaurus and Supersaurus were shaped much like Diplodocus or Apatosaurus). To estimate the weight of Supersaurus, take a Diplodocus model and divide its length (lm, about 1.5 feet) into the length of Supersaurus (ld, around 140 feet). ld/lm = 140 feet/1.5 feet = 93.3333 or a scale of about 1/93 Then follow the same procedure that you would for any other model.

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Learning the bones In this exercise you will need to learn the bones of the arms and legs. All vertebrate animals that live on land have the same basic arrangement of bones in their limbs. They have a single large bone in the upper arm (humerus) or upper leg (femur), two long bones in the lower arm (radius and ulna) or lower leg (tibia and fibula), small bones in the wrist (carpals) and ankle (tarsals), bones in the palm of the hand (metacarpals) and foot (metatarsals), and fingers and toes (digits).

FIGURE 2.23 Human (left) and crocodile (right) leg.

How was a dinosaur different from other reptiles? Living reptiles have a sprawling or semi-sprawling posture meaning that their legs are held out to the sides of their bodies. Dinosaurs, mammals, and birds hold their legs directly beneath their bodies in an erect stance. Because mammals, birds, and dinosaurs use their legs in the same way, we can look at the bones of living animals, whose relative speeds we know, to help determine the running speeds of dinosaurs.

FIGURE 2.24 Postures of a sprawling, semi-erect, and erect animals.

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FIGURE 2.25 Hind limbs of an armadillo (left), coyote (middle), and antelope (right).

Figure 2.25 shows the hind legs of three different mammals (an armadillo, coyote, and antelope) arranged according to speed and drawn so that the femur lengths are the same. The armadillo is the slowest and the antelope is the fastest. What observations can you make about how the legs differ as the animal gets faster? Based on your observations from the armadillo, coyote, and antelope legs, how fast do you think the animals in Figure 2.26 are? Which is fastest, slowest, and in between? Now let’s see if you are correct. Figure 2.27 shows how these animals would perform in a race. Now assess the speeds of the dinosaurs in Figure 2.28.

FIGURE 2.26 Skeletons of an antelope (A), coyote (B), horse (C) and elephant (D).

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FIGURE 2.27 A hypothetical race between some common animals.

FIGURE 2.28 Skeletons of a Stegosaurus (left), Camarasaurus (middle), and Struthiomimus (right).

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Hatching and death on Egg Island In our everyday life on land, we see little evidence of organisms in the act of being preserved as fossils. When living things die their bodies usually disappear in a short time. Other animals, such as bacteria and fungi, eat plants and animals. The complete decomposition of the bodies of dead organisms results in the production of gases and minerals. The “dust to dust” recycling of living things is the general rule. Sometimes in forests under fresh and decomposing leaves, we see black carbon-rich soil. Such soils retain some of the remains of organisms, but usually there are no clues as to which decaying plants, animals, bacteria or fungi contributed to the young soil. Perhaps the fact that we normally do not see fossils form, explains why some people have trouble understanding the presence of fish, shells, and trees in rock formations around the world. Notice whenever you go for a walk the bodies of plants and animals, the discarded parts of the organisms like leaves, shells, feces, footprints, or feathers. Perhaps you will have time to return to these sites again to observe the fate of these remnants of our time. Imagine how any one of these remains might endure for a time longer than others. Think about how fossil evidence of any one of these remains may last for a year, a century, a million years, or a thousand million years. If you ever thought about a cat waking across wet concrete, or leaf collection becoming buried in manmade airtight time capsule, think also about natural methods of preservation. The activities in this chapter are about ways fossils are preserved. The chances of any living creature leaving its mark on Earth in the form of a fossil are remote. Despite the great odds, under certain rare circumstances, organisms—in whole, in part, or as phantom clues—may survive in fossil form. Some fossil specimens survive in such great numbers, they make up mountains of fossiliferous rock, while in other instances, only a small part of a species might be found in fossil form. How many species (including living and extinct) have there been in the history of Earth? To estimate this number, assume there are 5,000,000 species of organisms alive today. Assume the average life span of a species is 2,000,000 years. Assume also, there is fossil evidence of life on Earth as early as 3,500,000,000 years ago, and that life originated on Earth about 3,800,000,000 year ago. It could be that as many as 2,000,000,000 species have lived on Earth. Paleontologists have identified and named only about 150,000 fossil species, or about 0.00008% of these species calculated to have lived on Earth in all of history. Thus, if only 1 in 12,000 extinct species has been found in fossil form, it follows that few species have fossilized. Or, does it instead mean that few of the fossils have been found?

Fossilization Taphonomy is the science that tries to explain how living organisms, their parts, tracks, and traces become fossils in the rock of Earth. Taphonomy addresses all the biological and physical processes that transform an organism as it leaves the biosphere and becomes established in the lithosphere.

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FIGURE 2.29 Dinosaur nesting site from about 75 million years ago.

The fates of organisms after death depend on many variables: where they die, how they die, the altitude of the land, the turbulence of the seawater, the fallout of a volcano, how palatable they are to other organisms, how quickly they become buried in sediments, and how mineralized is their skeletal structure. The list of conditions that favor fossilization is extensive. To get a handle on the processes by which a dying organism leaves evidence of its existence, we will illustrate the events of life and death as it occurred at the nesting sites of a species of hadrosaur during the late Cretaceous Period. Figure 2.29 depicts the fates of dinosaur eggs in nest sites of about 75 million years ago. Similar nest sites have been found in northern China, in the basins the Rocky Mountains

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of Montana and Alberta, and in southern France. Included in the figure are the fates of dinosaurs whose remains were found at the nest site. In the figure, the eggs in the nest on the hill are alive and just beginning to hatch. Notice that several babies are running around and several eggs are cracking. Bushes and boughs provide protective cover and bedding and possibly food. The nest is on high ground, possibly on an island of a continental lake or sea. Adults have been tending to the eggs. As the eggs hatch, shells are trampled, scattered and powdered by the babies. The younger members of the family then join the parents in migratory herds and return to the breeding site the following season. Predators eat some of the young; others die, rapidly decompose, and disappear. The same family will use the same nest site with a new layer of sediment again and again.

Things to note in Figure 2.29 1. On the left slope of the egg nest hill on the shoreline surface, are the skeletal remains of a carcass of an adult dinosaur partially immersed in water. No meat remains on the scattered bones. In the coming winter storms the now disassembled bones will be separately washed down the hill into a river where several of the bones and teeth remain today in an ancient sandstone delta of an inland sea. 2. The large dead dinosaur to the right of the egg nest succumbed to old age. Her flesh was partially eaten by tyrannosaurs and other scavengers. Carrion beetles, flies, and bacteria cleaned meat from some of the bones. Small mammals are gnawing through the bones for blood-making marrow. Pterosaurs pick at the bones for meat and calcium and phosphorus salts. The exposed dinosaur was completely recycled in two days. Nothing was left to fossilize. 3. The third dinosaur had the misfortune to stumble off the shoreline into shallow water. At this spot the deep sandy sediments were fine grained, rounded, and kept in a liquid-like state by up welling spring waters. The struggling young dinosaur thus sunk into quicksand and was deeply buried before it began to decompose and disintegrate. As millions of years passed, more layers of sediment accumulated on top of the dinosaur skeleton. Bacteria and fungi cleaned out the meat. Silicon-rich volcanic ash and lava eventually covered the overlying sediments. The open spaces in the bones filled with a form of agate called red jasper. Later much of the original bone dissolved and was replaced by other forms of silicates or calcite. As time passed these petrified bones of the dinosaur were compressed, heated, and deformed by the movement of moving plates. In time the deforming bones completely lost their identity as dinosaur bones, and became an indistinguishable part of the rocks. 4. Possibly several thousand years before the events on the egg nest site that were just described, a great flood occurred in the region of the breeding grounds. The waters of the sea of the great basin rose to flood many of the nest egg sites in the breeding ground of this species of dinosaur. You can see that one site still remained under water. The eggs at this site had not yet hatched

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at the time of the flood. The eggs were preserved in their original shape and appearance. A form of calcium carbonate from the water infiltrated the shell with a form of limestone. A few baby dinosaur bones have been recovered in the eggs. These dinosaur eggs were preserved by an almost instantaneous protection against destruction by predators, decomposition, and the elements of the water. Immediate burial in toxic water pickled the eggs during the first few days of their 75 million years internment as fossils in rock. Once buried sediments, and now rock, the eggs become subject to various physical and chemical changes. In this instance, the eggs became a true fossil in the original form, made of an original shell surrounding a calcium carbonate center with or without the remains of a developing dinosaur. In another instance, the shell disappeared, leaving an impression or replacement of mineral in the shape of the original specimen. The original fossil is replaced with a casting of a new chemical composition, known as pseudomorph. Whichever fate the eggs follow, the ultimate fate is deformation and the redistribution of minerals by natural geological processes.

Questions 1. The rains that wash the land and drain the tributaries of loose bones will carry them many miles from their source in the breeding ground. Along the way they will be scattered, a tooth here and a bone there, in the sand of a river. When the river slows, a large amount of debris—including a large amount of bones—will settle into a graveyard of bones collected from a large area. Of what possible use to paleontologists would a collection of such varied bones be? 2. One dinosaur weighed about 25 tons. It accumulated this mass by eating an enormous weight of leaves of the evergreen trees. And in less than two days scavengers (dinosaurs, pterosaurs, small mammals, insects, and bacteria) returned the carcass to dust without a trace. The scavengers then die and their flesh and bones are eaten and (in rare circumstance) they are preserved as fossils. What keeps the cycle going year after year, for as long as organisms have been on Earth? (The Sun and Photosynthesis) 3. The bones of every fossil do not last forever. The bone may be replaced by agate and calcite. Pretty soon you cannot tell fossil from rock, it turns into indistinguishable rock. Is this a fact? 4. Most of the fossils of dinosaur babies come from eggs that were of the Cretaceous Period. Fossils of Jurassic babies are few, and fossils of Triassic babies are rare. Why do you think that may be so? 5. After an egg loses its shell it has no protection from soil or water. Minerals from the soil or the water replace the internal content of the egg. The internal substance may look like an egg but it really is not—it is a pseudomorph. A pseudomorph may look exactly like an egg but inside of it is nothing but mineral. How would you proceed to make a pseudomoph of an egg?

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Predation Predation occurs when one organism feeds on another. Seashells, both fossil and recent, make excellent subjects to observe the effects of predation because many marine predators leave distinctive marks on the shells of their victims or prey. Knowledge of how to read these marks can make a trip to the beach seem like unraveling a crime story. Topic: Predator/Prey Moon snails are members of the family Naticidae (phylum Mollusca, class Gastropoda). Go to: www.scilinks.org They are found in marine waters all over the world, although they are more common in Code: AP006 areas that have sandy or muddy bottoms. Moon snails have a round shell that is actually too small for them to completely withdraw their bodies (Figure 2.30). Moon snails crawl along the surface or burrow within sand and mud in search of molluscan prey, usually clams FIGURE 2.30 and snails. They are very slow movers, so the prey must be equally slow in order to be run down. Once captured, Moon snail shell (left) and live moon snail (right) showing its “foot” and mantle. the prey is enveloped in the moon snail’s large foot and held while the moon snail drills a distinctive beveled hole (Figure 2.31) in the shell of the prey. It drills this hole by secreting acid onto a spot on the shell and then filing away the loosened material with its radula. Once the drill hole is complete, the moon snail inserts its

FIGURE 2.32 Shells of two species of Muricidae, which drill small, vertically sided holes in the shells of their prey.

FIGURE 2.31 Incomplete (left) and complete (right) drill holes in shells created by moon snails.

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FIGURE 2.33 Shell clipping crab attacking a snail.

proboscis into the shell and eats the flesh of the animal. The drilling process takes many hours during which the moon snail may be interrupted. If the prey escapes, it may have an incomplete drillhole. If the moon snail recaptures the prey, it will start drilling again, but in a new position. This may result in multiple drill holes. Therefore incomplete drill holes and multiple drill holes usually indicate that the moon snail had difficulty handling the prey. Snails of the family Muricidae (Figure 2.32) also drill holes in shells. These snails crawl on the surface of the sediment and look for prey that also live on the surface, like oysters and mussels. The drill holes of the murex shells can be distinguished from moon snail drills because they are not beveled and have straight sides as if the hole was excavated by a power drill. Many crabs feed on clams and snails. Some of these crabs attack the snail by carefully opening the shell along the whorl like a can opener (Figure 2.33). Victims of these attacks have a distinctive channel cut into the shell. Survivors of such attacks can be found with healed scars in the shell (Figure 2.34).

FIGURE 2.34 Shell of whelk that was damaged by a crab (left) and volute snail that survived a crab attack and regrew its shell (right).

Activity: Go to a beach with seashells or bring a bucket of shells into class. Look through the shells for the distinctive marks of predation. How many shells are drilled? Which of these drills are from moon snails and which, if any, are from murex shells? Calculate the percentage of drilled shells. In some places drilling can be as high as 30% of the population. Look for evidence of crab predation. How many shells have evidence of crab predation? How many survived the attack and regrew their shell? Do any of the snails show evidence of multiple attacks? Have any shells been attacked by both snails and crabs?

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What was the purpose of the plates on the back of Stegosaurus? FIGURE 2.35 Two living examples of animals with defensive armor; tortoise (top) and armadillo (bottom).

With its tiny head, huge plates and spiky tail, Stegosaurus is one of the strangest dinosaurs. The long, pointed, spear-like tail spikes were clearly for defense. But what about those plates on Stegosaurus’ back, were they for defense too? Let’s start our investigation of Stegosaurus by creating hypotheses about the purposes of the plates. Brainstorm some possibilities.

FIGURE 2.37 Scared cat arching its back and extending its fur to make itself look larger to enemies.

FIGURE 2.36 African porcupine showing its spiny defense.

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FIGURE 2.38 Puffer fish in its normal uninflated pose (bottom) and how it looks when threatened (top). Hypothesis 1: Defense/Armor. The plates serve as armor to thwart attack by predators. For example, turtles and armadillos are covered by plates (Figure 2.35). ◆ Hypothesis 2: Defense/Spikes. For example porcupines have sharp spines for protection (Figure 2.36). ◆ Hypothesis 3: Defense/Display. The plates make Stegosaurus look bigger to scare away predators. For example, many animals, such as cats, try to make themselves look bigger when they are scared (Figure 2.37). ◆

Some animals may combine these traits. For example when the puffer fish is frightened, it puffs up to make itself larger and is also covered with spines (Figure 2.38).

FIGURE 2.39 Male peacock shows off its plumage to a female.

Hypothesis 4: Courtship/Display. The plates are for attracting mates. For example male peacocks have large and elaborate feathers, which seem to be solely for attracting mates (Figure 2.39). ◆ Hypothesis 5: Thermoregulation. The plates allow Stegosaurus to collect and radiate heat. For example elephants are large animals that live in a hot environment. They use their large ears to help radiate the heat their body produces (Figure 2.40). ◆

Now let’s make observations and predictions about these different hypotheses. Observations in this case mean looking at the characteristics of each of the traits, e.g., are porcupine quills sharp or dull? Once you have described how those traits fit a

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FIGURE 2.40 Elephant and its ears, rich with blood vessels, which help radiate heat.

particular hypothesis, you test that hypothesis by making a prediction about Stegosaurus. For example: Porcupine spines are sharp, therefore if Stegosaurus plates were serving a protective function like porcupine spines do, you would expect Stegosaurus plates to be sharply pointed. If Stegosaurus plates are not sharply pointed (which they aren’t) then you reject the hypothesis that the plates served as that kind of defense. Hypothesis 1: Defensive armor. Observations: Turtles and armadillos have tough platy armor that covers their entire body. The underside of turtles is covered by plates. Armadillos have a soft belly, but this vulnerable area is protected by their habit of rolling up into a ball. Prediction: Stegosaurus plates will be tough and will cover the vital areas of the body. Hypothesis 2: Defensive spikes. Observations: Porcupine quills are sharp, stiff, barbed, and deter attackers by puncturing their skin. Prediction: Stegosaurus plates will be strong and pointed. Hypothesis 3: Defensive display. Observations: Animals have a variety of ways to make themselves look larger. They may raise their feathers or hair or puff up their bodies. The result is a much larger looking animal. When they are not scared they usually lower their defenses and return to their normal appearance. Prediction: Stegosaurus plates will make the animal look significantly larger and may be moveable. Hypothesis 4: Courtship display. Observations: In animals such as peacocks where large showy feathers attract mates, only the males have the large display feathers while the females are much drabber in appearance (this is called sexual dimorphism). Prediction: Male Stegosaurus will have large plates and females will have smaller plates or no plates at all.

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FIGURE 2.41 Skeleton of Stegosaurus.

Hypothesis 5: Thermoregulation. Observations: Elephant ears are large and thin and full of blood vessels. Blood is then pumped into these blood vessels and heat is radiated out of the animal through the thin skin of the ear. Prediction: Stegosaurus plates will be large and thin and full of blood vessel holes.

FIGURE 2.42 Stegosaurus plate showing its porosity and thinness.

Now let’s make some observations on Stegosaurus and test these predictions (Figure 2.41): 1. Stegosaurus plates are not attached to the skeleton; they are embedded in the skin of the animal. 2. They occur in two rows down the back in a staggered arrangement. 3. They are largest over the hip and smallest over the neck and the middle of the tail. 4. They are thin (Figure 2.42) 5. They are more or less five-sided, and though some have “points” they are not sharp enough to puncture an attacker’s skin (Figure 2.42). 6. They are full of blood vessels holes and very porous (Figure 2.42). 7. As far as we can tell (it is hard to tell the gender in dinosaurs from skeletons), Stegosaurus plates were not sexually dimorphic, i.e., both males and females had large plates.

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It is convenient to place these predictions and tests in a table: Hypothesis

Prediction

Test

Defensive Armor

Plates tough and cover vital areas

No: plates weak and do not cover sides

Defensive Spikes

Plates strong and sharp

No: plates weak and not sharp

Defensive Display

Plates make Stegosaurus look larger

Yes

Courtship Display

Males have plates, females don’t No: both sexes have plates

Thermoregulation

Plates thin and porous with many blood vessel holes

Yes

Conclusion: The plates fail our tests for defensive armor, spikes, and courtship display. They meet our predictions for defensive display and thermoregulation. Can we distinguish between these two hypotheses? Let’s look at the arrangement of the plates. They occur in two rows down the back in a staggered or offset pattern. If the primary purpose of the plates was to make the animal look larger, then the actual arrangement would not be important, i.e., they could occur in a single row or in two rows without overlap. However the arrangement may be important if the plates serve as heat collectors or radiators. Some scientists did an experiment in which they made metal models to simulate three different plate arrangements. One model had a single long fin running down the back, the second model had two rows of plates arranged directly opposite each other, and the third model had two rows of plates arranged in a staggered or offset pattern as in Stegosaurus. The surface areas of the plates were the same for all three models. They heated the models to the same temperature, put them in a wind tunnel and then measured how fast each of them radiated heat. The third model, with the plates in two staggered rows, radiated heat the fastest. This further supports the hypothesis that the plates were used for thermoregulation. But we still can’t definitively state the purpose of the Stegosaurus plates. While Stegosaurus is the only member of an entire group of armored dinosaurs with flat plates in two rows, it is difficult to imagine it had a unique metabolism from all its relatives. The exact purpose of the plates remains an unanswered mystery.

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Final Note: All scientific hypotheses are tentative. A new analysis with more information may yield a different result. Also, many body parts may serve multiple functions. The claws of a bear can be used for digging but they also make formidable weapons. Likewise, the plates on Stegosaurus may have served several purposes, e.g., heat regulation and defensive display.

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Mass Extinction and Meteor Collisions With Earth Introduction Earth is constantly bombarded by rocks from space. Rock sizes range from specks of dust, to pea-size pebbles, to boulders of many tons, to asteroids up to several kilometers in diameter and millions of tons in mass (Figure 3.1). Dust produces the often seen meteors or shooting Topic: Dinosaur Extinction stars, and boulders produce fireballs. The rare asteroids and comets cause catastrophic Go to: www.scilinks.org damage to Earth. Code: AP007 Most large meteors originate in the asteroid belt in orbit between Jupiter and Mars. They escape this orbit when asteroid collisions occur, or when strong gravitational forces from Jupiter perturb them into new Earth-crossing orbits. Space rocks may also come from the Moon or inner planets after major collisions with bolides (large meteors) on these nearby celestial bodies. For example 34 meteorites on Earth have been identified as having a Martian origin. Some space rocks are parts of FIGURE 3.1 comets that originate in outer regions of the solar system and move in Meteor entering Earth’s atmosphere. elliptical orbits around the Sun. Like the rocks of Earth, meteorites resemble in composition the core, mantle, and crust of Earth. In general, meteorites are either composed of iron-nickel or of stone... but there are stony irons. Even among the irons and the stones there are classes and subclasses. Stones are more abundant than irons. However, large iron meteors resist burning and breaking up as they enter the atmosphere better than do stones. The history of life on Earth is characterized by long periods of slow change punctuated by moments of rapid geological change. These rapid changes in Earth’s environments are attributed by some scientists to the effects of asteroid collisions. In such extreme geological moments mass extinctions occur, followed by adaptive radiations of survivors.

Causes of extinctions Over 99% of all the species that have ever lived are now extinct. This statement seems outrageous on the face of it, but let’s work it out. The average geological life span of a species is about 5 million years. Complex organisms large enough to be seen with the naked eye have been around for over 500 million years. Thus, there have been over a hundred “generations” of species on the planet, Earth on average replacing its organisms with new species every 5 million years. Therefore over 99% of all species that have lived are now extinct. Put in this simplistic way, extinction is a natural process that occurs all the time, right along with speciation or the evolution of new species.

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FIGURE 3.2 Geological time scale

But let’s look at extinction in more detail. Paleontologists divide extinctions into two broad categories: background extinctions and mass extinctions. Background extinctions occur continuously as a result of environmental changes, predation, competition, etc. They probably occur at a rate of 10’s to 100’s of species per year. Generally species that go extinct in this fashion have been replaced by the evolution of new species so that overall diversity, or the total number of species, has remained stable or increased. Mass extinctions are unusual in that they involve very large numbers (millions) of species, of very different kinds (e.g., clams, dinosaurs, plants) dying within a relatively short time. What is a short time? To a geologist, a short time means around 1–2 million years. Although some extinctions probably occurred over much shorter intervals, say hundreds to thousands of years, it is difficult to tell time with this much precision in the rock record. Often all we know is that the extinction took less than a million years. Mass extinctions mark turning points in evolution. The biggest extinctions not only killed a lot of species, they also altered the biological landscape so that the organisms and communities that took the place of the extinct ones were radically different. Geologists divide Earth’s history into intervals called eons, eras, and periods (Figure 3.2). The Phanerozoic Eon, which stared about 545 million years ago, is divided into 3 eras and 12 periods. During the Phanerozoic Eon there were five major mass extinctions and many smaller ones. The two biggest extinctions occurred at the Paleozoic-Mesozoic and Mesozoic-Cenozoic boundaries, and most other major extinctions occured at or near period boundaries. This is no coincidence. The geologic time scale was divided and named based on the great changes in life brought about by the extinctions. The extinction at the Mesozoic-Cenozoic boundary occurred about 65 million years ago. Its most famous victims were the dinosaurs, but many other groups went extinct including swimming and flying reptiles, many groups of mollusks, and many species of marine microplankton. Over

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half of all species went extinct at this time. What caused this extinction? There is a great deal of evidence that suggests it was caused by an asteroid impact. This evidence includes a giant impact crater buried beneath the surface of the Yucatán Peninsula in Central America. In addition, a variety of particles and elements that are indicative of an impact were deposited in rocks in the same sedimentary layer as the extinctions. What were the effects of the impact of this asteroid? Given an estimate of the mass and speed of the asteroid, the effects can be modeled (see Activities 2–4 in this chapter). For instance, if we assume the asteroid was 10 km in diameter (based on the size of the crater beneath the Yucatán Peninsula), and was traveling about 30 km per second (about the average speed of meteorites), and had the density of an average asteroid, then the energy released by its impact would be equal to about 10 billion 15-kiloton (about the size of the atomic bomb dropped on Hiroshima) atomic bombs. Or put another way, an energy release equivalent to covering every square meter of land on Earth with two tons of TNT. The effect of this much energy released in one place is fantastic. There is evidence of huge tsunamis emanating from the impact site and striking all around the Gulf of Mexico. There is evidence that the heat of the explosion ignited forest fires around the world. The smoke from these fires and the dust thrown into the atmosphere from the impact probably shut out sunlight and darkened the surface for months. The lack of light had disastrous effects on plant life, which in turn affected the herbivorous animals that ate the plants and then the carnivores that ate the herbivores. By destroying the plants at the base of the food chain, a vast chain reaction was set in motion that resulted in many of the world’s species dying out. Though the evidence is strong for an impact at the Mesozoic-Cenozoic extinction, evidence for impact as a cause is weak or lacking for most of the other extinctions. There have been many other causes proposed for these extinctions including massive volcanic eruptions, changes in sea level, and climatic cooling. Periods of widespread volcanism put huge amounts of carbon dioxide into the atmosphere. Carbon dioxide is a greenhouse gas, meaning it helps trap heat from the sun in our atmosphere, and sudden large inputs of this gas could quickly raise global temperatures. Overheating of Earth can cause extinctions by melting the polar ice caps and raising the sea level, slowing ocean circulation and upwelling, and by simply making it too warm for many species to survive. New species would evolve to live in these new oceans and in the warmer temperatures, but not before extinctions had occurred. There is some evidence that the Permian-Triassic extinction was the result of global warming and large expanses of volcanic lava erupted at about this time. Sudden cooling can also cause extinctions. It is well known that fewer species of plants and animals live in polar and temperate regions than in the tropics. So a climatic event that turns a largely tropical world into a temperate or polar one will cause many extinctions. There is a great deal of evidence that suggests that extinctions at the end of the Ordovician Period and in the Mid-Cenozoic were caused by global cooling. Sea

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Topic: Asteroids Go to: www.scilinks.org Code: AP008

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level changes can cause extinction by drowning a previously dry continent, and thus killing the animals that lived on the continent, or by exposing an area that was previously underwater and thereby killing the marine life that inhabited the former ocean. At several times in Earth’s past, vast areas of the continents have been flooded or exposed. Half of North America was underwater at some time during the age of the dinosaurs. To make matters more complicated, both global warming and cooling will affect sea level by melting or growing the polar ice caps, so several different causes may act in concert to cause an extinction.

TEACHER’S NOTES: Answers to questions in Activity 2: QUESTION 1:

Answer: The mass of the meteor can be calculated by multiplying its volume by its density. Let’s assume the meteor is a sphere. The volume of a sphere is 4/3πr3. Iron/nickel has a density of about 8 grams per cubic centimeter. Therefore the mass of the meteor = (4/3)(3.1416)(0.05cm)3 (8g/cm3)=0.0042g or 0.0000042kg. The kinetic energy can be calculated with the equation KE = ½ mv2 = (0.05)(0.0000042kg)(32000m/sec)2 = 2150 Joules. Energy released is the equivalent of 0.51 calories, about the energy you get from four ounces of diet soda. QUESTION 2:

Answer: Convert tons to kilograms: 1 kilogram = 2.2 pounds, therefore 50 tons = (50 tons)(2000lbs/ton)/2.2kgs/lb = 45454.5 kg KE = (0.5)(45454.5kg)(32000 m/sec)2 = 2.33 x 1013 joules. To help put this in perspective, a thousand tons of TNT (1 kiloton) has an energy yield 4.2 x 1012 Joules. Therefore 2.33 x 1013 joules is about the yield of 5,000 tons of TNT. QUESTION 3:

Answer: Convert miles to centimeters and find the volume of the asteroid: 6 miles = (6mi)(5280ft/mi)(30.5cm/ft) = 966240cm. Volume = 4/3πr3 = (4/3)(3.1416)(483120cm)3 = 4.72 x 1017 cubic cm. (Volume)(density) = mass Mass = (4.72 x 1017cc)(8g/cc) = 3.8 x 1018g or 3.8 x 1015kg. KE = (0.5)(3.8 x 1015kg)(32000m/sec)2 = 1.95 x 1024 joules. (Additional energy released after impact originates from such exothermic reactions as the burning of trees and sulfur.) Let’s put 1.95 x 1024 joules in perspective: The atomic bomb dropped on Hiroshima has a yield of 20 kilotons of TNT. Therefore, the Hiroshima A-bomb had an energy yield of (20)(4.2 x 1012 joules) = 8.4 x 1013 joules. If we divide this figure into the kinetic energy of our six-mile asteroid, we find that its impact would release the energy equivalent of 23 billion A-bombs. That is enough to strap four A-bombs onto every man, woman and child on the planet. QUESTION4:

Answer: KE = (0.5)(63000tons)(2000lbs/ton)/2.2lbs/kg) (10mi/sec)(5280ft/mi)(0.305m/ft)2 = 7.4x1015 joules This is the energy equivalent of 90 Hiroshima atomic bombs.

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Searching for micrometeorites Researchers estimate between 100 million and 8 billion tons of micrometeorites fall on Earth annually (Figure 3.3). Much of this dust is magnetic iron-nickel that can be collected and examined.

Procedures:

M AT E R I A L S : ◆ spoon ◆ cup ◆ zip-lock bag

1. Collect several spoons full of dirt from the base of a drain spout or a rain gutter of a house ◆ magnet or other building. Tile roofs are best since they do not produce other particles, and they ◆ magnifying lens drain well. Pour the dirt into a cup. Dry the dirt. Place a strong magnet in a plastic bag. Run ◆ microscope and slides the bagged magnet through the collected dirt allowing magnetic dirt to cling to the plastic ◆ petroleum jelly bag. Release the magnetic dirt into a white dish. Use a microscope to search for spherical ◆ HCl or smooth objects that may have flamed and melted when they entered the atmosphere, forming droplets as they cooled. An alternative technique is to use a piece of transparent tape ◆ nitric acid to pick up the magnetic particles from the white dish, and view the strip with a microscope. ◆ NH4OH 2. Catch micrometeorites on a greased slide. Thinly coat a microscope slide with petroleum ◆ citric acid jelly. Heat the slide to obtain a thin uniform film. Expose the slide to the sky where it will ◆ dimethylglyoxime be undisturbed for 24 hours. Examine the slide under high magnification. Look for spherical ◆ heater shiny bodies. Estimate the number of similar particles falling on the entire Earth in one day, 18 2 noting that the total surface area of Earth is 5.10x10 cm . Collect a sample of particles settling ◆ test tubes from the air onto a tray for a day or more. Weigh a small magnet to 0.1 mg. Sweep the tray ◆ medicine droppers with the magnet to pick up all magnetic particles. Weigh the magnet with iron particles. The ◆ beakers difference is the weight of presumed micrometeorites. Remove magnetic particles from magnet ◆ funnels with transparent tape. Using the values of weight or particles, area of the tray, and the area of Earth’s surface, calculate the mass of magnetic micrometeorites falling to Earth each year. ◆ filter paper 3. Test your micrometeorites for nickel metal. Since elemental nickel hardly ever occurs in terrestrial FIGURE 3.3 rock, the detection of nickel in a rock is a good test for a meteorite. Wearing goggles, rubber gloves, and Micrometeorites; scale bar on left is 200 microns, working in a hood, dissolve, in separate test tubes, less scale bar on right is 100 microns. than a gram of meteoritic rock, some iron, some nickel, and suspected micrometeorites in heated concentrated HCl. When dissolved, add a few drops of concentrated nitric acid. Immediately add several drops of citric acid to prevent the iron from precipitating. Neutralize with NH4OH. Filter the solution if it is not clear. Test for nickel by adding a few drops of a 1% alcohol solution of dimethylglyoxime. When nickel is present the solution turns a bright cherry red.

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Calculating the energy of incoming rocks from space M AT E R I A L S : ◆ calculator ◆ balance and weights ◆ real or substitute meteorite

Topic: Meteors Go to: www.scilinks.org Code: AP009

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Procedure: You can calculate the energy of a moving object when you know the mass and velocity of the object. Use the equation: Kinetic Energy (in joules) = (0.50)(mass in kilograms)(velocity in meters/second squared), or K.E. = ½ mv2. For example, suppose a 60-gram ball falling at a velocity of 2 meters per second splashes into a pond. How much energy was transferred from the ball to the pond at impact? Answer: K.E. = (0.50)(.06kg)(2meters/second)2 = 0.12 joules. Since there are 4180 joules in a (food) calorie, the energy released by this collision is equivalent to 0.0000029 calories Let us now calculate the energies of three sizes of rocks from space as they collide with Earth. 1. Most meteors (shooting stars) are mere specks, the size of grains of sand, when they crash into Earth’s atmosphere. But their energy is great enough to produce bright lights that streak across the sky. Suppose a particular micrometeorite entered the atmosphere as an iron/nickel sphere with a diameter of 1.0mm at a velocity of 32,000 meters/second. How much energy is released? 2. Suppose a fireball-producing meteor with a mass of 50 tons enters the atmosphere at 32,000 meters/second. How much energy will it release? 3. Suppose an iron/nickel asteroid six miles in diameter crashes into Earth at a velocity of FIGURE 3.4 32,000 meters/second. How much energy Meteor Crater in Arizona. of motion does it release to Earth? 4. The Arizona meteor crater formed in an instant about 50,000 years ago (Figure 3.4). Although the meteorite was vaporized on impact, scientists estimate that the meteorite had a mass of 63,000 tons, a diameter of about 80 feet and a velocity of 10 miles per second. About how much energy was transferred from meteorite to Earth during this collision?

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Modeling impact craters Introduction

M AT E R I A L S :

A look at the surfaces of inner planets, moons, and asteroids in our solar system reveals numerous scars of meteor impacts. Even Earth shows evidence of extensive cratering during the past 600 million years. Since Earth is subject to continuous weathering, craters tend to fill up and erode into obscurity faster than those on our airless moon or the planet Mercury. Scientists have a lot of questions about how impact craters form. True impacts are rarely seen. Most studies of cratering are limited to simulations of impacts in laboratories using “meteorites” of small mass and low velocity. In this activity you will be working in such a laboratory.

◆ sandbox

Procedures:

◆ video camera

1. Fill a sandbox (about 50cm by 100cm square), or a tiny tot’s wading pool, with fine grain sand to a depth of about 30cm. Support a rod about 2 meters above the sand. Fix an electromagnet above the sand with an off/on switch on the line (Figure 3.5). The magnet should be strong enough to support steel spheres of the various masses available. 2. Release a steel ball (by turning off the electromagnet) so it falls freely into the sand. Record the mass of the ball, the diameter of the ball, the height the ball falls, the diameter of the crater made, the depth of the crater, and the depth of the penetration of the ball into the sand. 3. Repeat the collisions using steel spheres of different sizes. Record all data. Search for relationships between masses and the results of the impacts. 4. Now repeat the tests changing the height the sphere falls. Calculate the energy of impact by measuring the mass of the sphere and its velocity at impact using K.E. (in Joules) = 1/2mv2. Terminal velocity of a free falling mass = 2gh. The kinetic energy of a 50g sphere falling from a height of 2.5m is (0.5)(0.05kg)(7m/ sec) = 0.175 Joules. What relationship can you see between energy and crater diameter?

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◆ sand ◆ crushed limestone ◆ assorted steel spheres ◆ electromagnet ◆ switch ◆ ruler

FIGURE 3.5 Apparatus for simulating impacts.

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A N A LY S I S : Attributes Trial 1:

Mass of sphere

Trial 2: Trial 3: Trial 4: Trial 5: Trial 1:

Height above sand

Trial 2: Trial 3: Trial 4: Trial 5: Trial 1: Trial 2:

Crater diameter

Trial 3: Trial 4: Trial 5: Trial 1: Trial 2:

Crater depth

Trial 3: Trial 4: Trial 5: Trial 1:

Depth of penetration

Trial 2: Trial 3: Trial 4: Trial 5: Trial 1:

Sand/ limestone

Trial 2: Trial 3: Trial 4: Trial 5: Trial 1: Trial 2:

Eject patterns

5. If you become interested in studying ejecta patterns, you may want to substitute pulverized limestone for sand. The limestone holds together better than sand, and thus shows rays, secondary craters, and blankets or ejecta. The patterns of rays formed around craters can be more easily studied by sprinkling iron filings over the surface of the sand or limestone before impact. Preparing sand with alternating layers of colored sand enables the researcher to trace the ejection of sand at various depths from the impact site. Unfortunately the test mixes the sand, preventing one from reusing the sand in layers experiments. You should videotape these one-time events. Videotaping impacts is useful in observing the details of crater formation. Videotaping has the additional advantage of enabling the viewer to see events in slow motion. Crater specialists have a lot of questions to answer. One of their biggest problems is figuring out the size of a space rock from the diameter of the crater it left behind. From your laboratory experiment, what would you guess was the size of a meteorite that made the 1.2 kilometer in diameter crater in Arizona 50,000 years ago?

Trial 3: Trial 4: Trial 5:

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What happens when the energy of an asteroid or comet is released in the rock and atmosphere of Earth? Procedure: Table 3.1 records the diameters, locations, and ages of selected craters.

TA B L E 3 . 1 Selected List of Authenticated Impact Craters Worldwide.

1. Search for a relationship between these impact craters and events in the history of life on Earth comparing them to the Geological Time Scale in Figure 3.2. 2. What events occurred around the times these large craters known as astroblemes or “star wounds” formed on Earth’s surface. 3. Close your eyes and imagine the crash of the asteroid or comet on South Africa about 250 million years ago. Where did all the energy of the giant meteorite go? How did the solid Earth respond physically? How did the atmosphere respond? What happened to the ice caps? The plants, animals, and other organisms? What percentage of living species do you think became extinct? Why do you think that many of the species which evolved after the cataclysm were different from those that lived before? 4. Create a piece of art that communicates the role of asteroid collisions in the evolution of Earth and life.

More than 150 impact craters have been identified worldwide and newly identified craters continue to be added to the list each year. Almost all the structures exhibit a variety of evidence pointing to impact origin. Most are visible on the surface. The ten listed here are among the largest or the best known on the planet. The type of evidence is tabulated as follows: (1) shock metamorphism; (2) coesite or stishovite (rocks that formed by impact); (3) shatter cones; (4) raised rim or a central uplift; (5) ring structure; (6) shattered rock breccia or a breccia lens; (7) impact melt or impactite glass; (8) meteorites or meteoritic oxide.

Name & Location Acraman (Australia)

Chesapeake Bay (Virginia, USA)

Chicxulub (Yucatan, Mexico)

Kara-Kul (Tajikistan)

Manicouagan Lake (Quebec, Ontario)

Meteor Crater (Arizona, USA)

Poigai Basin (Siberia, Russia)

Ries Basin (Bayern, Germany)

Sudbury Structure (Ontario, Canada)

Vredefort Ring (South Africa)

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Diameter (miles)

Evidence (type)

Age (MYA)

Visible on Surface?

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